1. Field of the Invention
The present invention relates to a shift control system and a shift control method making a switch between shift ranges of a transmission via an actuator.
2. Description of the Background Art
A shift control system based on a technique sometimes called “shift-by-wire” has been known. The shift control system switches the shift range of an automatic transmission under electrical control according to operation of a shift lever by a driver. Under this shift control system, when the driver operates the shift lever, a shift-range switch instruction is generated to energize an actuator and thereby rotate a detent plate. When the detent plate reaches a predetermined rotational position, the detent plate and a detent spring engage with each other to determine a shift range. The detent plate engaging with a roller of the detent spring has a plurality of depressions corresponding respectively to different shift ranges (see Japanese Patent Laying-Open No. 2002-323127 for example).
When the shift range is changed by the above-described shift control system, the roller of the detent spring climbs over a protrusion of the detent plate and then down to be fit in a desired depression so that a desired shift range is determined. It is thus necessary to stop the detent plate at a position which allows the roller to be fit surely in the depression. If the detent plate is incorrectly positioned, the roller could be pushed against the protrusion or any of the laterally outermost walls of the detent plate and consequently the detent plate stops while the detent spring is flexed. In this case, the recovery force of the detent spring causes needless rotation of the detent plate so that the shift range could be moved to an undesired position. Moreover, vibrations of the vehicle could cause the detent plate to move and thereby move the shift range to an undesired position.